Upscaling factor estimation on pre-JPEG compressed images based on difference histogram of spectral peaks

Abstract Image is one of the most widely used information carrier exchanged in the Internet, which raises a problem of privacy leakage. Private images are vulnerable to be intercepted and altered by an attacker, violating the owner’s privacy. When an image is tampered maliciously, it is often necessary to perform geometric transformations such as scaling to hide the traces of tampering, introducing resampling traces. In the last two decades, spectral analysis is the most commonly used method for resampling detection. However, since JPEG compression severely interferes the statistical characteristics of resampled images and introduces blocking artifacts, the robustness is really poor for most classical spectrum-based methods in the presence of JPEG compression. In this paper, we propose a method to estimate the upscaling factors of upscaled images in the presence of JPEG compression. A comprehensive analysis in spectrum of scaled images is given. We find that both the location and their difference of spectral peaks in the spectrum of the upscaled pre-JPEG images are related to the upscaling factor. Hence, we adopt the difference histogram of spectral peaks to screen candidate upscaling factors and obtain the final estimation by additional verification step according to the location of the spectral peaks. The experimental results demonstrate the effectiveness of the proposed method.